Methodological approaches to population based research of screening procedures in the presence of selection bias and exposure measurement error: colonoscopy and colorectal cancer outcomes in Ontario.

Background: The study describes the methodological challenges encountered in an observational study estimating the effectiveness of colonoscopy in reducing colorectal cancer (CRC) incidence and mortality.

Methods: Using Ontario provincial administrative data, we conducted a population-based retrospective cohort study to assess CRC incidence and mortality in a group of average-risk subjects aged 50-74 years who underwent colonoscopy between 1996-2000. We created two study cohorts; unselected and restricted.

Effect of colonoscopy on colorectal cancer incidence and mortality: an instrumental variable analysis.

Background: Using population-based health services information to estimate the effectiveness of colonoscopy on colorectal cancer (CRC) outcomes is prone to selection bias.

Objective: To determine the effect of colonoscopy on CRC incidence and mortality.

Design: Population-based retrospective cohort study.

Social disparities in the use of colonoscopy by primary care physicians in Ontario.

Background: It is unclear if all persons in Ontario have equal access to colonoscopy. This research was designed to describe long-term trends in the use of colonoscopy by primary care physicians (PCPs) in Ontario, and to determine whether PCP characteristics influence the use of colonoscopy.

Methods: We conducted a population-based retrospective study of PCPs in Ontario between the years 1996-2005.

Betel quid without tobacco as a risk factor for oral precancers.

The IARC monographs recently classified chewing betel quid without tobacco as a human carcinogen. Several studies in Taiwan have reported that betel quid without tobacco may increase the risk of oral precancers such as oral leukoplakia and oral submucous fibrosis. However in India, since most betel quid chewers prefer to add tobacco to the quid, the independent effect of betel quid on the risk of oral precancers is difficult to assess and has not yet been fully explored.

Risk factors for multiple oral premalignant lesions.

Oral leukoplakia, oral submucous fibrosis and erythroplakia are 3 major types of oral premalignant lesions. Multiple oral premalignant lesions may possibly develop due to field cancerization, where carcinogenic exposures can cause simultaneous genetic defects to the upper aerodigestive tract epithelium, putting the epithelium at high risk for development of premalignant lesions at different stages of carcinogenesis. There have been no epidemiological studies on risk or protective factors of the disease.

Interim results from a cluster randomized controlled oral cancer screening trial in Kerala, India.

A cluster randomized controlled oral cancer screening trial is on-going in the Trivandrum district, India, to evaluate the efficacy of screening in reducing oral cancer mortality. Subjects, aged 35 years and above, in 13 clusters in the Trivandrum district, India, were randomized to the intervention (screening) group (7 clusters, 78969 subjects) to receive three rounds of screening by oral visual inspection by trained health workers at 3-year intervals or to a control group (6 clusters, 74739 subjects). Two rounds of screening were completed between 1995 and 2002 during which 69896 (88.